The present invention relates to data storage, and more particularly, to an apparatus and method for a scalable Network Attached Storage (NAS) system.
With the increasing popularity of Internet commerce and network centric computing, businesses and other organizations are becoming more and more reliant on information. To handle all of this data, various types of storage systems have been developed such as Storage Array Networks (SANs) and Network Attached Storage (NAS). SANs have been developed based on the concept of storing and retrieving data blocks. In contrast, NAS systems are based on the concept of storing and retrieving files.
A typical NAS system is a single monolithic node that performs protocol termination, maintains a file system, manages disk space allocation and includes a number of disks, all managed by one processor at one location. Protocol termination is the conversion of NFS or CIFS requests over TCP/IP received from a client over a network into whatever internal inter-processor communication (IPC) mechanism defined by the operating system relied on by the system. Some NAS system providers, such as Network Appliance of Sunnyvale, Calif., market NAS systems that can process both NFS and CIFS requests so that files can be accessed by both Unix and Windows users respectively. With these types of NAS systems, the protocol termination node includes the capability to translate, e.g., CIFS requests into whatever communication protocol is used within the NAS system.
The file system maintains a log of all the files stored in the system. In response to a request from the termination node, the file system retrieves or stores files as needed to satisfy the request. The file system is also responsible for managing files stored on the various storage disks of the system and for locking files that are being accessed. The locking of files is typically done whenever a file is open, regardless if it is being written to or read. For example, to prevent a second user from writing to a file that is currently being written to by a first user, the file is locked. A file may also be locked during a read to prevent another termination node from attempting to write or modify that file while it is being read.
A disk controller handles a number of responsibilities, such as accessing the disks, managing data mirroring on the disks for back-up purposes, and monitoring the disks for failure and/or replacement. The storage disks are typically arranged in one of a number of different well known configurations, such as a known level of Redundant Array of Independent Disks (i.e., RAID1 or RAID5).
The protocol termination node and file system are usually implemented in microcode or software on a computer server operating either the Windows, Unix or Linux operating systems. Together, the computer, disk controller, and array of storage disks are then assembled into a rack. A typical NAS system is thus assembled and marketed as a stand-alone rack system.
A number of problems are associated with current NAS systems. Foremost, most NAS systems are not scaleable. Each NAS system rack maintains its own file system. The file system of one rack does not inter-operate with the file systems of other racks within the information technology infrastructure of an enterprise. It is therefore not possible for the file system of one rack to access the disk space of another rack or vice versa. Consequently, the performance of NAS systems is typically limited to that of single rack system. Certain NAS systems are redundant. However, even these systems do not scale very well and are typically limited to only two or four nodes at most.
There are other drawbacks associated with individual NAS systems. For example, individual NAS systems all have restrictions on the number of users that can access the system at any one time, the number of files that can be served at one time, and the data throughput (i.e., the rate or wait time before requested files are served). When there are many files stored on an NAS system, and there are many users, a significant amount of system resources are dedicated to managing overhead functions such as the locking of particular files that are being access by users. This overhead significantly impedes the overall performance of the system.
Another problem with existing NAS systems is that the performance of the system cannot be tuned to the particular workload of an enterprise. In a monolithic system, there is a fixed amount of processing power that can be applied to the entire solution independent of the workload. However, some workloads require more bandwidth than others, some require more I/Os per second, some require very large numbers of files with moderate bandwidth and users, and still others require very large total capacity with limited bandwidth and a limited total number of files. Existing systems typically are not very flexible in how the system can be optimized for these various workloads. They typically require the scaling of all components equally to meet the demands of perhaps only one dimension of the workload such as number of I/Os per second.
Another problem is high availability. This is similar to the scalability problem noted earlier where two or more nodes can access the same data at the same time, but here it is in the context of take over during a failure. Systems today that do support redundancy typically do in a one-to-one (1:1) mode whereby one system can back up just one other system. Existing NAS systems typically do not support the redundancy for more than one other system.
A NAS architecture that enables multiple termination nodes, file systems, and disk controller nodes to be readily added to the system as required to provide scalability, improve performance and to provide high availability redundancy is therefore needed.